A. Field Of The Invention
The present invention relates to a process for producing an oil and water adsorbent polymer in broken microparticle form capable of entrapping any desired solid and/or liquid oleophilic and/or hydrophilic compound and composition (organic and/or aqueous) for delivery. More particularly, the present invention relates to a process for producing a highly porous and highly crosslinked hydrophilic/oleophilic polymer in the form of open (broken) spheres and sphere sections characterized by a mean unit particle size of about 0.5 to about 3000 microns, preferably about 1 to about 300 microns, more preferably about 0.5 to about 100 microns, and most preferably, for cosmetic uses, about 0.5 to about 80 microns. The microparticles have an oil sorbency of at least about 72% by weight, preferably at least about 80% by weight (calculated as weight of material sorbed divided by total weight of material sorbed plus dry weight of polymer sorbent). The present invention is also directed to the oil and water adsorbent microparticles produced by the process having an extremely low bulk density in the range of about 0.008 gm/cc to about 0.1 gm/cc, preferably about 0.009 gm/cc to about 0.07 gm/cc, more preferably about 0.0095 gm/cc to about 0.04-0.05 gm/cc. The microparticles produced by the process of the present invention are capable of holding and releasing oleophilic oils, creams, cleaners, medicaments, and other organic active compounds and compositions, as well as hydrophilic active compounds and aqueous compositions, individually, or both oleophilic and hydrophilic materials simultaneously, for use in the cosmetic, cleaning, chemical process, and pharmaceutical industries.
B. Background
Early disclosures of polymer particles appear in U.S. Pat. Nos. 3,493,500 and 3,658,772. These patents disclose the production of aqueous suspensions of polymer particles from acrylic acid monomer and/or acrylamide monomer in an aqueous reaction medium at pH 1-4. Both patents teach that the result in polymer suspensions, which were not characterized as to particle size or structure, were suitable for use as flocculating agents for sewage treatment.
It was subsequently discovered that polymers could be made in a porous particulate form by a variety of techniques. The art has stated that "the type of polymerization technique used is an important factor in the determination of the resulting product." See U.S. Pat. No. 4,962,170 at column 2, line. 4. As stated in U.S. Pat. No. 4,962,170 at column 2, lines 7-11, "within each type of polymerization, there are procedural alternatives which can have significant impact on the resulting product" "[t]he differences in the polymerization techniques are enough that a procedure used in one type of polymerization technique that will not necessarily have the same effect if used in another polymerization technique." Thus, there is a significant degree of unpredictability in the art.
Porous polymeric particles are capable of being prepared by one of two processes, i.e., precipitation polymerization in a single solvent system, or suspension polymerization in a two phase liquid system. The precipitation polymerization technique is disclosed in U.S. Pat. Nos. 4,962,170 and 4,962,133. U.S. Pat. No. 4,962,170 discloses a precipitation polymerization process wherein the disclosed monomers are soluble in the single solvent system, and the resulting polymer, which is insoluble, precipitates out of solution once a critical size is obtained. In the disclosed process, the solution of monomer consists exclusively of one or more types of polyunsaturated monomer. Because each monomer is polyunsaturated, each monomer also functions as a crosslinker, resulting in a highly crosslinked polymer particle.
U.S. Pat. No. 4,962,133 also utilizes the precipitation polymerization process for producing a porous polymeric particle. However, unlike the above-described process, wherein the monomer solution consists exclusively of polyunsaturated monomers, the process of U.S. Pat. No. 4,962,133 discloses that the monomer solution can include one monosaturated monomer in combination with one polyunsaturated monomer, wherein the polyunsaturated monomer can comprise up to 90% by weight of the total weight of monomers. Because the precipitation polymerization technique relies upon the formation of polymer aggregates of precipitated polymer particles, the monomer solution is not vigorously agitated during polymerization in order to avoid separation of the aggregated polymer particles.
U.S. Pat. No. 5,316,774 is directed to a suspension polymerization process, again limited to a maximum of 90% by weight polyunsaturated monomers, based on the total weight of monomers. Accordingly, it is an object of the present invention to provide a process for making sorbent microparticles from a monomer solution that contains more than 90%, preferably about 92% to 100%, by weight, polyunsaturated monomers, based on the total weight of monomers in the monomer solution.
The process of U.S. Pat. No. 4,962,133 is limited to a solvent system that is an aqueous/organic azeotrope. Because the organic solvent cannot be separated from the water in an azeotrope, azeotropic solutions present special waste disposal problems. Accordingly, it is an object of the present invention to provide a process for making oil and water adsorbent microparticles that do not require an azeotropic solution. Further, the particles produced by the process of U.S. Pat. No. 4,962,133 range extensively in size from less than about 1 micron in average diameter for unit particles to about twelve hundred microns in average diameter for clusters of fused aggregates. The large variability in size limits the utility and properties of the polymeric particles. Accordingly, it is also an object of the present invention to provide a process for making polymeric microparticles of a less diverse size distribution.
Another process disclosed in the art for producing microscopic polymeric particles is in situ suspension polymerization wherein an active ingredient included within the monomer mixture is retained in the formed polymer upon completion of polymerization. Examples of in situ suspension polymerization include U.S. Pat. No. 4,724,240, wherein polymerization of a monounsaturated monomer and a polyunsaturated monomer in an aqueous/polyvinylpyrrolidone system containing an emollient, as the active agent, produced relatively large microparticles, having a mean diameter "between 0.25 to 0.5 mm" (i.e., 250 to 500 microns), that contain the emollient therein upon completion of polymerization. A problem with a particle having a mean diameter of 250-500 microns is that the particle is capable of being sensed by touch. This is an undesirable property if the particle is to be used in a lotion, cream, or other cosmetic formulations. Accordingly, it is also an object of the present invention to provide a process that is capable of manufacturing polymeric particles having a smaller mean diameter, e.g., about 0.5 .mu.m to about 120 .mu.m, preferably about 1 .mu.m to about 100 .mu.m, for a smoother skin feel.
A second problem with the process of U.S. Pat. No. 4,724,240 is that it is limited to those active ingredients that are capable of dissolving in the organic solvent. Further, the active ingredient(s), which may be proprietary, are provided in bulk to the polymer manufacturer so that they can become trapped in the particles during the polymerization process. To overcome these problems, it is a further object of the present invention to provide polymeric microparticles having evacuated internal pores, within broken (open) microparticle spheres and sphere portions that are capable of adsorbing both oleophilic and hydrophilic solids and liquids in higher amounts than prior art microparticles. It is theorized that the oleophilic solids and liquids are adsorbed within the interior porous surface area of each open sphere or sphere portion, in large amounts, so that they may be loaded within the interior of the spheres with adsorbed active oleophilic organic ingredient(s) in solid or solvent-dissolved form, and it is theorized that the exterior porous surface area of the broken spheres adsorb both hydrophilic and oleophilic solids and liquids via capillary adsorption in the porous outer surface (oleophilic materials) or by surface attraction of hydrophilic materials.
The polymeric microparticles of the present invention are capable of adsorbing both (a) organic compounds and organic compositions containing oleophilic compounds dissolved in an organic solvent, as well as solid organic compounds entrapped within an interior of the open (broken) microparticle sphere pores; and (b) liquid hydrophilic compounds and hydrophilic aqueous compositions containing water-soluble compounds dissolved in water, as well as solid hydrophilic solid compounds that are adsorbed on an exterior, porous surface area of the broken spheres.
A third problem with the process of U.S. Pat. No. 4,724,240 is that it is not suited for use when the active ingredient is a mixture of components that differ significantly from one another as to oleophilicity. In such a situation, the more oleophilic of the active ingredients would be selectively isolated in the pores of the polymer made by the process of U.S. Pat. No. 4,724,240. To overcome this problem, the process of U.S. Pat. No. 4,724,240 would have to be separately applied to each of the active ingredients, and thereafter, the resulting products would be mixed. Such additional processing and mixing is costly. Accordingly, it is a further object of the present invention to provide a process for producing a microparticle wherein the microparticle is capable of receiving a plurality of oleophilic active ingredients and/or a plurality of hydrophilic active ingredients.